The immune deficiency of leukemic mice will be studied in the view of suppressor cells described in our laboratory. We will experiment with the effect of these leukemic suppressor cells on the immune functions of both T and B cells, both in vitro and in vivo. The cellular mechanisms of this suppression will be explored. BIBLIOGRAPHIC REFERENCES: Cerny, J., Proffitt, M.R. and Essex, M. Immunosuppression by Moloney leukemia virus: Lack of correlation between virus replication and the immunosuppressive effect. J. Nat. Cancer Inst. 56:819, 1976. Forger, J.M., III and Cerny, J. Thymic hormone modulation of leukemogenic virus replication. Cancer Res. 36:2048, 1976.